Recovery and decomposition of mgcl2



De 31, 1946. N. c. CHRISTENSEN 2,413,292

RECOVERY AND DECOMPOSITION OF MgCl Dilure MgC l2 soluh'on PRELIMINARY EVAPORATOR I MgO f1 Dilure o2 MgClz solufion SPRAY ABSORBER K I L N CONCENTRATOR 4\ G MILL hm gases M90 7 1 5- DISINTEGRATOR 7 e h Hcl 3 HCl solurion o 1 (12 or Dry C12 I CONDENSOR wQsre D ECOMPOSI NG gases FURNACE superhec1red 9 srecm or air 7 gmwm MgO o r (MgOHCD Dec. 31, 1946. N. c. CHRISTENSEN 2,413,292

RECOVERY AND DECOMPOSITION OF MgClg 4 Sheets-'-Sheet 2 N. C. CHRISTENSEN RECOVERY AND DECOMPOSITION 0F MgCl Filed Jan.- 17, 1944 4 Sheets-Sheet 3 Figly.

N. c. CHRISTENSEN:

RECOVERY AND DECOMPOSITION OF MgCl Filed Jan. 17, 1944 4 Sheets-Sheet 4 Patented Dec. 31, 1946 RECOVERY AND DECOMPOSITION OF MgCl2 Niels C. Christensen, Salt Lake City, Utah, assignor to Combined Metals Reduction Company, Salt Lake City, Utah, a corporation of Utah Application January 17, 1944, Serial No. 518,618

Claims. (Cl. 23-201) This invention relates to recovery of MgCh from solution and the decomposition of the MgClz to secure MgO or Mg(OH)Cl and HCl or MgO and chlorine. As is well known to chemists and metallurgists, MgClz when heated in the presence of steam decomposes to form MgOI-ICI and HCl, or MgO and HCl, and when heated in the presence of oxygen decomposes to form MgO and C12 as indicated in the following chemical The first reaction begins at approximately 200 C., the reaction being very slow at this temperature but, becomes more rapid with increase in temperature until at 450 C. to 500 C. the reaction is very rapid and, under proper conditions, may be made substantially complete in a short period of treatment. The second reaction begins at approximately 500 C. and is very rapid at 650 C. or higher temperatures and, under proper conditions, may be made substantially complete in a relatively short time. The third reaction begins at a temperature below 100 C. but is extremely slow at low temperatures, the reaction becoming more rapid with increase in temperature until at 650 C. the decomposition.

is very rapid, and may be made complete in a relatively short period under proper conditions of treatment. Studies on the equilibrium conditions in these reactions show that relatively concentrate HCl and C12 gases may be secured at temperatures above 600 C., and that relatively small amounts of heat are required for the decomposition, the first reaction being slightly exothermic (+5100 cal.), the second being quite endothermic (20700 cal.) and the third slightly endothermic (-5600 at 600 C.). In spite of the apparent ease of decomposition of MgClz, numerous commercial attempts to utilize the above reactions to secure MgO and HCl or chlorine have failed on account of the lack of understanding of the conditions necessary for the successful economic carrying out of such a process. The main difficulties encountered in the process have been due, first, to the difiiculty of securing a dry or substantially solid MgClz by the methods commonly used and, second, to the failure to use methods and apparatus in the decomposition which would make possible the use of a minimum of steam or air (oxygen), so as to avoid excess waste of heat and to secure a concentrated H0] or C12 gas. The first difilculty, that of securing 2 a solid MgClz product, led to attempts to secure decomposition directly from the MgClz solution, such attempts being doomed to failure on account of the excessive heat requirements, the limited period of treatment possible, the very dilute HCl gases secured and the poor decomposition ob- Y tained. Attempts to decompose the solid product also failed due to failure to understand the requirements necessary for complete and rapid decomposition and for the securing of a relatively concentrated HCl gas.

The difiiculties encountered in securing a solid product from solutions containing the MgClz have been due to the partial decomposition of the MgClz in hot concentrated solutions and the sticking of the solid product to the drying or heating surfaces as a cement-like mass. The difficulties encountered in the attempts to decompose the solid product With steam, have been due to the use of apparatus in which no efiective contact of steam and MgClz were secured, and in which also no segregation of the steam and the HCl was maintained, so that a minimum of steam might be used and a concentrated HCl gas might be secured. The difficulties encountered in securing a solid MgClz are overcome in my process by the method of evaporation used to secure the final concentrated MgClz solution, and the recovery of the MgClz in a solid mixed MgClz MgO product (and not as a relatively pure MgClz product), and the difficulties encountered in the decomposition process are overcome, by the countercurrent treatment of the dry MgClz MgO product with steam (or air) in such a manner, that an eifective segregation of the steam (or air or oxygen) is maintained, so as to make possible the use of a minimum of steam (or air or oxygen) and thus secure a complete decomposition and a concentrated HCl (or C12) gas.

The method of carryin out the process is illustrated in the accompanying flow sheet, Fig. I, and set forth in detail in the following description. The diagrammatic illustrations of the preferred type of multiple effect evaporator, and the decomposing furnace preferred for use in the process, are shown in Figs. II, III and IV, Fig. II showing a vertical section of the evaporator, Fig. III a longitudinal vertical section of the decomposing furnace and Fig. IV showing in enlarged cross-section a detail of the furnace.

Th process consists in general of three steps: (1) the concentration of the MgClz solution, (2) the formation of the solid MgClz MgO product and (3) the decomposition of the MgClz in the MgClz MgO product.

1. Concentration of the M gC'lz solution The concentration of the MgClz solution is pref erably carried out in two stages, particularly, if the original solution is somewhat dilute. In the first stage the solution is preferably evaporated in a multiple effect evaporator or, if fuel is cheap or hot waste gases are available, in a spray type evaporator, indicated as preliminary evaporator I on the flow sheet, Fig. I. The multiple effect evaporator may be of the type shown diagrammatically in Fig. II, or of any. other suitable type. The spray evaporator may be of the type shown in my U. S. Patent 1,462,363 (or, of any other suitable type). The relatively, dilute solution in is first evaporated to form a relatively concentrated solution in the preliminary evaporator I. If this evaporation is carried out in the preferred type of apparatus of Fig. II, the operation is conducted as described below. The multiple effect evaporator of Fig. II consists of a verti cal series of jacketed evaporating chambers or effects A, B, C, D. Each of these chambers consists of a central cylindrical solution chamber IOI surrounded by an annular steam chamber I02, the two chambers being separated by the heat transfer wall I03. Each chamber or effect is supplied with a vertical central pipe I04 which passes through the top I of each effect and extends nearly to the bottom I06 of the chamber. Evaporated solution from each chamber is passed from the chamber through the outlet pipes I01 which connect with the center of the bottom I05 of each chamber. Steam from each evaporating chamber IOI escapes through the outlet pipes I08. The solution level I09 in each solution chamber IOI is regulated by the float valves I II) which prevent escape of steam through the outlet pipes I08 until the solution level I09 is low enough that the valve falls away from its seat at the lower end of the pipe I 08. Steam is admitted to each steam chamber or jacket I02 through the inlet pipes I II which connect with the upper part of the chamber I02. Condensate from each jacket or steam chamber I02 escapes through the outlet pipes II2, the escape being controlled by the float valves I I3 which are seated upon the upper end of the pipes II2 so that the pipe is opened only when the condensate level is such as to lift the float valve from its seat. Condensate is admitted to each jacket I02 through the condensate inlet pipes II4. effects are connected in a complete vertical column by joining the solution outlet pipes I01 from each upper effect to the inlet pipe I04 of the effect below, the steam inlet pipes I II of each upper effect to the steam outlet pipes I08 of the effect below, and the condensate outlet pipes II2 of each lower effect to the condensate inlet pipes I I4 of each upper effect. In the lower part of each solution chamber is a centrally located solution circulator or agitator II5 mounted on the central shaft II 6 which is suspended from a,

suitable bearing II! at the upper end of the uppermost column I04 which is closed by the cover H8. The shaft H6 is driven by the sheave or pulley I I 9 so as to circulate the solution in the chamber IOI as indicated by the arrows. Solution from the supply tank I20 is supplied to the uppermost solution chamber IOI through the inlet pipe I2 I, the supply being regulated by the float valve I22 so as to maintain thelevel in the upper solution chamber IOI as indicated. Concentrated solution from the lowermost chamber IN is discharged from the main vertical outlet The separate pipe I23 through the fioat controlled outlet valve I24 and outlet pipe I25, the height I being so proportioned to the height II that the concentrated solution in column I approximately balances the solution in column II, but with sufficient difference to cause a flow of solution upward through the outflow pipe I23 which is regulated by the valve I24. superheated steam under the required pressure is supplied to the jacket I02 of the lowermost effect through the steam inlet pipe III. To start the apparatus, air is completely displaced from the jackets I02 by admitting sufficient live steam through the valves I26 and I2! to displace and drive all the air out of the jackets through the valve I28, and from the main outlet pipe I23 and solution chambers IOI by closing the outlet valve I23 and release valve I30 and inlet valve I22 and outlet valve I35, and admitting sufficient live steam through the valves I3I and I32 to displace all the air through the valve I33. When the air has been completely displaced from the apparatus, the steam inlet valves I26, I3I and I 32 and steam outlet valves I28 and I33 are closed and the solution (11 which is preheated and boiled to remove any air by means of the steam coils I34 in the supply tank I20, is then admitted to the apparatus and allowed to gradually fill the chambers from the bottom upward while live steam, under sufficient pressure and superheat to boil the solution at the desired final concentration, is supplied thrOugh the steam inletpipe III and valve I21. the solution has filled the chambers and column as indicated in the drawings, the normal operation of the apparatus is as follows: The agitating device is placed in operation. The steam supplied to the jacket I02 of the lowermost effect D condenses and evaporates the concentrated solution in the solution chamber IOI of the effect D under the pressure of the liquid in the column, and the steam from the solution chamber under thispressure passes through pipes I00 and III into the jacket I02 of the effect C, where it condenses and evaporates the less concentrated solution in. the solution chamber of this effect,

sending. the steam from this effect through the pipes I08 and III into the jacket of the next effect B, where it condenses and evaporates the less concentrated solution in the solution chamber IOI of this effect, and sends the steam from this chamber through the pipes I08 and III into the jacket I02 of the uppermost effect A, where it condenses and evaporates the incoming solution, sending the steam from this solution out i through the pipe I08 and valve I to the coils I34of the inlet tank I20 to preheat and boil the solution. The condensate from the jacket I02 of the lowermost effect D accumulates until the float valve II3 opens, allowing the condensate to flow up through the pipes H2 and H4 into the jacket I02 of the effect C, the condensate in this effect being similarly forced upward into B and that in B into A, from which it is finally discharged through the condensate outlet H2 of this uppermost effect. It will be seen that, as the solution is evaporated in passing down the successive stages or effects, the pressure of the steam in the effect increases, the steam of highest pressure being in thermal contact with the most concentrated solution which requires the highest temperature for evaporation. As the concentration of the solution in the evaporating column builds up, a regulated flow of solution is allowed to flow out of the outlet pipe I through the valve I35 until the column I23 is entirely filled When with concentrated solution, after which, the valve I35 is left open and the discharge of solution is regulated by the float valve I24. As previously noted, the apparatus should be so designed that the solution in column II is very slightly heavier than the concentrated solution of column I so that, as the solution is concentrated in the effects A, B, C, and D, it is forced up the column I23- and out through the valve I24. To secure any desired variation in the concentration of the outfiowing solution, several outlet valves and pipes I24, I35, and I25 at different levels may be,

supplied, the ones not in use being closed by their respective valves I35.

The point to which the evaporation in the preliminary evaporator is carried depends upon the type of evaporator used. If carried out in a multiple effect evaporator, it is not economical to carry the concentration much beyond a 35% MgClz solution, but, if carried out in a spray evaporator, the concentration may be carried to 50% MgClz or higher.

The partially concentrated solution b from the preliminary evaporator, or the already partially concentrated solution from any other source, is

mixed with sufiicient finely divided MgO from the decomposing furnace 6 to absorb the HCl and form MgClz, the solution as from the absorber being sent to the preliminary evaporatoror to the kiln concentrator 2 if no preliminary evaporator is used. g

2. Formation of a solid M 9012 M 90 product The thick, syrupy, concentrated, barely fluid solution 0 from the kiln concentrate is 'mixed with sufficient finely divided MgO p from the decomposing furnace 6 in the pug mill 4 to form a solid mixed product of MgClz-MgO. The

amount of MgO required in this operation depends upon the concentration of the MgClz solution 0 from the kiln concentrator" 2", Thepug; mill 4 is constructed with a cover so that hot gases I from a suitable furnace, or waste gases from the decomposing furnace, may be passed through the mill in countercurrent to the MgClz-MgO to secure a product d which issufficiently dry so that it may be readily broken up in the disintegrator 5. If theMgClz is tobedecomposed to form C12, this product d must be dried more thoroughly than if MgClz is to be decomposed to form HCl since, any water in the mixture going to the decomposing furnace 6 will form HCl.

3. Decomposition of the MgCZa The dried MgClz-MgO product (I from the pug mill 4 is broken down to approximately a6 or 8 mesh product in the disintegrator 5. At this size a substantially complete decomposition ofthe MgClz in the product may be secured in a relatively short time of treatment. If; ground much finer the charge is less porous and not as, permeable to the decomposing gases as the coarser product, and if too coarse, requires a longer time for complete decomposition of the;

MgClz. v p v The crushed MgClz MgO product e is heated to 600 C.-650 C. or higher, if desired, in, the decomposing furnace and treated with superheated steam g to form MgO and HCl, or with preheated air or oxygen g to form MgO and C12.

To secure rapid and complete decomposition of the MgClz with a minimum amount of steam or air, the decomposition must be carried out in a muffle type furnace, and the MgClz MgO product must be passed through the furnace in countercurrent to the steam or air andfurther, the;

MgClz MgO product must be brought into intimatemixture and contact with the steam or air. Also, for maximum. efliciency, the movement of the MgCla-MgO product must be sufficiently upward and the movement of the gases sufiiciently downward, to avoid mixture of the H01 with the steam, or C12 with the air, which occurs if the movement of the MgClz VIgO mixture is downward through the furnace and the movement of steam .or air is upward. Since the I-ICl is twice as heavy as the steam, and the C12 is considerably over twice as heavy as the oxygen or air if the decomposing gases are compelled to move upward the tendency of the heavier gases. (HCl or C12) is to move downward mixing with the incoming steam or air;,whereas, ifthe decom-* posing gases (steam or air) move downward, this position chamber 2M.

mixture is avoided as the heavier acid gases tend to move ahead of the lighter decomposinggases, thus preventing their mixture and increasing the efficiency of the steamer air in the decomposi-- tion of the MgClz and reducing theJrequired.-ex-' cess of steam or oxygen to a minimum. The

effect is important in the decomposition with" steam but, is especially noticeable and important in the decomposition with air (oxygen).

To secure these important factors in the decomposition of the MgClz, a furnace of the type shown in Fig. III is preferred, though the decomposition may be carried out in other types of furnaces as later mentioned. The furnace of Fig. III consists of a rectangular sloping decomposition chamber or mufile 20I, the bottom 202 of.

which consists of the upper wall of the lower heating space 283, and the top 294 of which consists of the lower wall 284 of the upper heating space 285. The muflle or heat transfer walls 202 and 2M consist of any suitable refractory material such as fire brick, Alundum, or Carbofrax. The s de walls of the decomposition chamber (not shown) are not heated but are solid exterior Walls, through which the rabble shafts enterthrough suitable glands to prevent escape of 1 gases from the furnace. The MgCh -MgO product d2 is fed into the lower end of the decomposition chamber 20I of the furnace from the feed hopper 206 by means of the plunger feeder 2M, and the decomposing charge is moved through the furnace to the upper end of the decomposition chamber by the horizontal rabbles 288; the MgO be is discharged from the discharge hopper 209 by means of the rotary water cooled discharge feeder ZIIl. Both the feed hopper 206 and discharge hopper 299 are at all times kept partly filled with the 1VIgC12 MgO and the MgO', so as to prevent escape of gases from the decom- Steam or air (oxygen) 02 for the decomposition of the MgClz is admitted to the decomposition chamber 2M through the perforated pipe 2I I. which extends across the upper end of the decomposition chamber20l and out through the side wall of the chamber; The HCl, or C12, are withdrawn from'the decomposing chamber 281 through the perforated pipe 212, which extends across the lower end of thechamber 201, and out through the side wall of the chamber to the connection to the condenser, or furnace, or spray leacher in which the H'Clor Cl: is to be utilized. Hot furnace gases are admitted to the heating spaces 203 and 205 through the lateral inlet openings 213 and 214 in the upper ends of the heating spaces 205 and 203, and the waste gases are discharged from these heating spaces through the lateral'outlet openings 215 and 216. (If desired, a number of "lateralinlet openings such as 213 and 214 may be spaced longitudinally along the sides of the heating spaces 203 and 295 to admit hot furnace gases, so as to maintain a more uniform temperature in'the decomposition space 201, or the hot furnace gases may be admitted through the openings 215 and 216 and discharged through the openings 213 and 214, so as to secure a concurrent flow of charge and heating gases.) The charge of MgClz MgO product is passed upward through the sloping decomposition chamber 201, in countercurrent to the decomposition gases (steam or air) (or oxygen), by the horizontal rabbles 288 shown in enlarged cross section in Fig. IV. The rabbles 2B8 consist of a suitable refractory material (such as Carbofrax, Alundum, etc), or suitable alloy not affected by HCl gas, or substantially the cross section shown in the figure. The rabbles are ri idly mounted on the hollow shaft 301 and held in position on the shaft 381 by the keys 3H2. The rabbles are arranged in two alternate series A: and Be, the rabbles A3 being stationary while the rabbles B3 move and the rabbles B: being stationary while the rabbles A3 move. The action of the rabbles is as follows: The rabbles B3 having completed a half revolution in the direction indicated by the arrow 03 and having lifted and dropped a load of material 93 in front of the lower arm of the rabble as indicated by the arrow e3, comes to rest in a fixed inclined position Xs-Xz as shown. The rabbles A3 then move through a' half revolution in the direction indicated by the arrow (23, scooping up the material as and lifting it and allowing it to rundown in front of the rabble A3, as indicated by the arrow is and rabble in dotted outline, to be picked up by the next rabbles B3 in the same manner and so on longitudinally through the decomposition chamber, being thoroughly mixed andbrou'ght into intimate Contact with the decomposing gases in each lifting and running operation. The rate of movement of the charge through the furnace is regulated'by the movement of the rabbles and must be so proportioned to the length of the decomposition chamber, as to allow suificient time of treatment to secure the required degree of decomposition. By this countercurrent movement of the charge up the sloping chamber and of the downward flow of gases in contact with the thoroughly mixed charge, a rapid and complete decomposition of the MgClz with a minimum of steam or air (oxygen) is secured.

If desired a straight line furnace of the type described but without the upper heating chamber 295 and with rabbles supported on shafts extending through the roof of the chamber 201 (such as is in use for roasting ores) may be used for the decomposition, and may secure good results if ma'deion; a slope as described, but will require a longer time of treatment than with the furnace described, due to the much less effective mixing and'contac't with the decomposing gases securedby these commonly used rabbles and method of rabbling. If an excess of decomposing gas is not deleterious in the uses to which the HCl or C12 is composing operation.

The steam g, or air, may be superheatedby the hot waste gases 0 from the decomposing furnace 6. Waste gases 0 from the decomposing furnace 6 may also be used, as indicated at k, for evaporation of the water in the MgClz solution in the kiln concentrator 2 and for drying, as indicated at l, the Mg'Clz MgO in the pug mill, thus reducing the amount of fuel required in the process. The HCl gas or C12 h from the decomposing furnace 6 may be used directly as such in leaching or precipitation processes without further treatment or, the HCl may be condensed to form an HCl solution 1 in the condenser I or the Ch may be dried in the condenser 1 to remove moisture and secure dry C12 7', previous to its use in chloridizing ores or for other uses.

What is claimed is: p

1. The process of forming a solid MgClz MgO product from a Mg'Clzsolution and of decomposing the MgClz in said product, which consists in,

heating and evaporating said solution to form a hot very concentrated barely fluid solution, mixing said last olution with sufiicient finely divided.

and HCl, which consists in passing a relativelyfinely crushed product containing MgClz upward through a sloping longitudinal heated chamber in countercurrent to an oxidizing gas passed downward through said chamber.

3. The process of forming a-solid MgClz Q MgO product from a MgClz solution and of decomposing the MgClz in said product, which consists in heating and evaporating said solution to form a hot very concentrated barely fiuid solution, mixing said last solution with suflicient finely divided MgO to form a solid MgClz MgO product, crushing said product to a relatively fine condition and passing said product upward through a sloping longitudinal externally heated chamber in countercurrent to steam passed downward through said chamber, thereby decomposing the MgClzlin. said product and forming MgO and HCl, and. using part of said MgO to form more MgClz MgO product for decomposition as described.

4. The process of forming a solid-MgClz MgO product from a MgClz solution and of decomposing the MgClz in said product, which consists in heating and evaporating said solution to forma hot very concentrated barely fluid solution, mixing said last solution with sufficient finely divided MgO to form a solid MgClz MgO product, passing hot gases over the mixture during said mix-, ing operation to dry'the MgClzproduct, crush ing said last product to a relativel fine condition, passing said product upward through a sloping longitudinal and externally heated chamber in countercurrent to gas containing free oxygen passed downward through said chamber, thereby decomposing the MgClz in said product and forming MgO and chlorine, and using part of said MgO product to form more MgClz MgO product as described.

5. The process of treating Mg'Clz to form MgO and HCl, which consists in passing a relatively finely crushed product containing MgClz upward through a sloping longitudinal heated chamber in countercurrent to steam passed downward through said chamber.

6. A process according to claim 5, in which the chamber is externally heated.

7. The process of treating MgClz to form MgO and C12, which consists in passing a relatively finely crushed product containing MgClz upward through a sloping longitudinal heated chamber in countercurrent to gas containing free oxygen passed downward through said chamber.

8. A process according to claim 7, in which the chamber is externally heated.

9. A process according to claim 1, in which the evaporation takes place in a plurality of stages.

10. A process according to claim 1, in which the evaporation takes place in a plurality of stages, one of said stages comprising multiple effect evaporation.

NIELS C. CHRISTENSEN. 

